It is usual for orthodontic brackets to be equipped with a transverse slot for receiving the arch wire, and with a peripheral groove for retaining the annular resilient tie ligature which serves to hold the arch wire in place in the transverse slot. In the usual prior art bracket, the ligature extends around the entire periphery of the bracket in a peripheral groove provided for that purpose. In accordance with the present invention, however, the tie ligature is supported entirely in the peripheral groove extending around the incisal portion of the bracket, so that the portion of the peripheral groove extending around the gingival portion of the bracket may be eliminated, and the incisal-gingival dimension of the bracket may be substantially reduced.
One of the embodiments of the invention to be described comprises a bracket equipped with lateral mesiodistal extending hooks at each end for temporarily retaining the ligature while the arch wire is being inserted into the transverse slot in the bracket, with the upper end of the ligature being supported in the peripheral groove extending around the incisal portion of the bracket. After the arch wire is in place, the lower end of the ligature is removed from the lateral hooks and doubled over the arch wire and inserted into the peripheral groove around the incisal portion of the bracket, so that both ends of the ligature are held in that groove. The lateral hooks may also be used to provide necessary anchorage for tooth rotation and translation thus enabling a reduction in the width of the bracket, in addition to the reduction in the height as described above.
The force exerted on the arch wire by the doubled-over configuration of the tie ligature in the appliance of the present invention provides a greater seating force on the arch wire into the transverse slot of the bracket as compared with the force exerted by the tie ligature extending around the periphery of the conventional bracket. This results in a greater control over the tooth by the arch wire which is firmly held in the depth of the transverse slot by the practice of the teaching of the present invention.
The resulting smaller bracket of the invention is aesthetically superior to the prior art brackets, and it is less likely to irritate the lips, cheeks, tongue or gingival tissue of the patient.
Because the gingival portion of the bracket of the invention can be reduced in dimension, the functional portion of the bracket may be placed closer to the gingival tissue, than is the case with the prior art brackets, reducing the likelihood of interference by the occlusion of the patient's teeth during mastication.